1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine capable of controlling the opening of a throttle valve so as to obtain a target amount of intake air.
2. Description of the Related Art
In recent years, there has been proposed a control apparatus for an internal combustion engine that can obtain excellent driving performance by using, as a requested value of a driving force from a driver or a vehicle side, the output shaft torque of the internal combustion engine (hereinafter also referred to simply as an engine) which is a physical quantity directly acting on the control of the vehicle, and by deciding, as an output target value of the engine in the form of the output shaft torque, engine control quantities in the form of an amount of air, an amount of fuel and ignition timing.
In addition, it is generally known that a control quantity having the greatest influence on the engine output shaft torque among the engine control quantities is the amount of air, and there has also been proposed a control apparatus for an internal combustion engine that is capable of controlling the amount of air with a high degree of precision (see, for example, a first patent document: Japanese patent application laid-open No. H11-229904).
In the above-mentioned first patent document, in the control apparatus for an internal combustion engine that controls the opening of a throttle valve by driving an actuator provided in association with the throttle valve, a target throttle effective opening area is calculated by applying a target amount of intake air corresponding to a target engine torque to an orifice flow rate expression which is based on a differential pressure across the throttle valve, an air passing area, and a specific throttle opening is set so as to attain the target throttle effective opening area thus calculated.
Thus, when the throttle opening that attains the target amount of intake air is calculated by applying it to the orifice flow rate expression, the target amount of intake air can be adequately attained even in cases where an environmental condition such as an atmospheric pressure, an intake air temperature, etc., has changed, or where exhaust gas recirculation (hereinafter referred to as “EGR”) for introduction of an exhaust gas into an intake pipe is carried out.
In the conventional control apparatus for an internal combustion engine, for example in case of the first patent document, in a throttle valve of which an effective opening area changes in accordance with the operating state of the engine, a flow coefficient, which greatly influences the shape and the opening area of the throttle valve, is obtained from the number of revolutions per minute of the engine and the pressure ratio of an intake pipe internal pressure (hereinafter referred to as an “intake manifold pressure”) and the atmospheric pressure. As a result, it is difficult to accurately set the flow coefficient in a state in which the degree of opening and an effective opening area of the throttle valve are not decided.
Accordingly, there is the following problem. That is, the target throttle effective opening area to obtain the target amount of intake air can not be calculated accurately, so there arises a deviation between the target amount of intake air and the actual amount of intake air, and besides a lot of labor is required to obtain the flow coefficient and to set a map therefor.
In view of the above, it can be considered that the target throttle effective opening area in the form of the product of the throttle effective opening area and the flow coefficient is calculated by applying the target amount of intake air to the orifice flow rate expression which is based on the differential pressure across the throttle valve, the air passing area, and the flow coefficient, and the target throttle opening is calculated by using the relation between the effective opening area and the throttle opening which are suited to each other in advance, so that a throttle opening to obtain the target amount of intake air is thereby calculated without setting the flow coefficient. In this case, however, there is the following problem. That is, even with the same throttle opening, there will arise a variation in the actual opening area and/or the flow coefficient resulting from the manufacturing variation of individual throttle bodies, etc., so the amount of intake air changes depending upon the individual throttle bodies.
Further, there takes place a variation in the calculated effective opening area due to the variation and/or estimation error of various kinds of sensors that measure the intake manifold pressure, the atmospheric pressure, the intake air temperature, etc. As a result, there is a problem that there arises a variation in the actual amount of intake air with respect to the target amount of intake air due to the variation of the throttle body and the various kinds of sensors, various kinds of estimation errors, etc.